User terminal and processor for transmitting UE EUTRA capability information

ABSTRACT

A mobile communication system is a mobile communication system that supports D2D communication that is direct device-to-device communication, and includes a user terminal configured to establish a radio connection with a base station, where the user terminal transmits terminal measurement information indicating information obtained by measurement of the user terminal, to the base station, and a network including the base station instructs the user terminal to start the D2D communication, when it is determined on the basis of the terminal measurement information that interference to the base station does not exceed a permissive amount when the user terminal performs the D2D communication.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of U.S. patentapplication Ser. No. 14/768,414 filed Aug. 17, 2015, which is a NationalStage Application of International Patent Application No.PCT/JP2014/053195 filed Feb. 12, 2014, which claims benefit of U.S.Provisional Application No. 61/766,461 filed Feb. 19, 2013, the entirecontents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a mobile communication system thatsupports D2D communication, abase station, a user terminal, and aprocessor.

BACKGROUND ART

In 3GPP (3rd Generation Partnership Project) which is a project aimingto standardize a mobile communication system, the introduction of Deviceto Device (D2D) communication is discussed as a new function afterRelease 12 (see Non Patent Document 1)

In the D2D communication, a plurality of neighboring user terminalsperform direct radio communication in a frequency band assigned to amobile communication system. In addition, the D2D communication is alsocalled Proximity Service communication.

CITATION LIST Non-Patent Document

Non Patent Document 1: 3GPP technical report “TR 22.803 V12.0.0”December 2012

SUMMARY

The current specifications have no mechanism for appropriatelycontrolling the D2D communication. Thus, when the user terminal freelyperforms the D2D communication, the base station may receiveinterference caused by the transmission power of the user terminal inthe D2D communication.

Therefore, the present disclosure provides a mobile communicationsystem, a base station, a user terminal, and a processor, with which itis possible to restrain interference to a base station by a userterminal that performs D2D communication.

A communication system comprises a user terminal and a base station,wherein the user terminal transmits UE EUTRA capability informationincluding information indicating an only uplink band on which the userterminal supports direct communication between terminals, to the basestation, to enable the base station to determine, on the basis of the UEEUTRA capability information, whether the user terminal supports thedirect communication, the user terminal receives, from the base station,information on radio resources to perform the direct communication, andthe user terminal controls: starting the direct communication based onthe received information on radio resources; measuring Reference SignalReceived Power (RSRP) of a received signal from the base station duringperforming the direct communication; and ending the direct communicationin response to the RSRP being higher than a predetermined value.

A user terminal comprises a transmitter, a receiver, and a controller,wherein the transmitter is configured to transmit UE EUTRA capabilityinformation including information indicating an only uplink band onwhich the user terminal supports direct communication between terminals,to a base station, to enable the base station to determine, on the basisof the UE EUTRA capability information, whether the user terminalsupports the direct communication, the receiver is configured toreceive, from the base station, information on radio resources toperform the direct communication, and the controller is configured tocontrol: starting the direct communication based on the receivedinformation on radio resources; measuring Reference Signal ReceivedPower (RSRP) of a received signal from the base station duringperforming the direct communication; and ending the direct communicationin response to the RSRP being higher than a predetermined value.

A processor, communicatively coupled to a memory, is configured tocontrol user terminal, wherein the processor executes processes oftransmitting UE EUTRA capability information including informationindicating an only uplink band on which the user terminal supportsdirect communication between terminals, to a base station, to enable thebase station to determine, on the basis of the UE EUTRA capabilityinformation, whether the user terminal supports the directcommunication; receiving, from the base station, information on radioresources to perform the direct communication; controlling starting thedirect communication based on the received information on radioresources; controlling measuring Reference Signal Received Power (RSRP)of a received signal from the base station during performing the directcommunication; and controlling ending the direct communication inresponse to the RSRP being higher than a predetermined value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of an LTE system.

FIG. 2 is a block diagram of UE.

FIG. 3 is a block diagram of eNB.

FIG. 4 is a protocol stack diagram of a radio interface in the LTEsystem.

FIG. 5 is a diagram showing a data path in cellular communication.

FIG. 6 is a diagram showing a data path in D2D communication.

FIG. 7 is a diagram for explaining an operation of a mobilecommunication system according to a first embodiment.

FIG. 8 is a sequence diagram showing an operation example of the mobilecommunication system according to the first embodiment.

FIG. 9A is a diagram for explaining a distance between eNB 200; and UE100-1 and the UE 100-2. FIG. 9B is a diagram for explaining receivedpower intensity and reception quality of a signal received by each ofthe eNB 200, the UE 100-1, and the UE 100-2.

FIG. 10 is a sequence diagram showing an operation example of a mobilecommunication system according to a modification of the firstembodiment.

FIG. 11 is a sequence diagram showing an operation example of a mobilecommunication system according to a second embodiment.

FIG. 12 is a sequence diagram showing an operation example of a mobilecommunication system according to a third embodiment.

FIG. 13 is a sequence diagram showing an operation example of a mobilecommunication system according to a modification of the thirdembodiment.

DESCRIPTION OF THE EMBODIMENT Overview of Embodiment

A mobile communication system according to an embodiment is a mobilecommunication system that supports D2D communication that is directdevice-to-device communication, and includes a user terminal configuredto establish a radio connection with a base station, where the userterminal transmits terminal measurement information indicatinginformation obtained by measurement of the user terminal, to the basestation, and a network including the base station instructs the userterminal to start the D2D communication, when it is determined on thebasis of the terminal measurement information that interference to thebase station does not exceed a permissive amount when the user terminalperforms the D2D communication. As a result, when the network determinesthat the interference to the base station exceeds the permissive amountwhen the user terminal performs the D2D communication, the user terminaldoes not start the D2D communication, and therefore, it is possible torestrain the base station from receiving interference from the D2Dcommunication by the user terminal.

In a first embodiment, the terminal measurement information is locationinformation indicating a location measured by the user terminal, and thenetwork determines, on the basis of a distance that extends between thebase station and the user terminal and that is evaluated from thelocation information, whether the interference to the base station doesnot exceed the permissive amount. As a result, the network is capable ofmaking a determination irrespective of an accidental change in radioenvironment in a base station or a user terminal, and thus, it ispossible to make a stable determination.

In a first embodiment, the terminal measurement information is radioenvironment information indicating a radio environment measured by theuser terminal, and the network determines, on the basis at least one ofa received power intensity that is received by the user terminal andthat is evaluated from the radio environment information, and a pathlossbetween the base station and the user terminal, whether the interferenceto the base station does not exceed the permissive amount. As a result,the network is capable of making a determination on the basis of anactual radio environment of the user terminal, and thus, it is possibleto improve the accuracy in determination.

In a first embodiment, the user terminal transmits D2D supportinformation indicating whether the user terminal supports the D2Dcommunication, the network determines, on the basis of the D2D supportinformation, whether or not the user terminal supports the D2Dcommunication, and the network does not instruct the user terminal tostart the D2D communication, when the user terminal does not support theD2D communication. As a result, the network does not need to request, tothe user terminal that does not support the D2D communication,unnecessary terminal measurement information for determining whether theD2D communication is to be performed by the user terminal.

In a first embodiment, when the network determines that the interferencefrom the user terminal to the base station does not exceed thepermissive amount and the user terminal performs communication withanother user terminal by way of the network, the network instructs theuser terminal and the other user terminal to start the D2D communicationeven when there is no request for the D2D communication from the userterminal and the other user terminal. As a result, the user terminal andthe other user terminal perform the D2D communication, and thus, it ispossible to reduce a load of traffic at the base station.

In a first embodiment, the network transmits confirmation informationfor confirming whether to consent to perform the D2D communication, tothe user terminal, and the network instructs the user terminal and theother user terminal to start the D2D communication when there is theconsent to perform the D2D communication from the user terminal. As aresult, it is possible to restrain the network from forcedly performingthe D2D communication by the user terminal against an intension of auser using the user terminal.

In a first embodiment, the network instructs the user terminal to startthe D2D communication, when the D2D communication is performed only in astate where the user terminal establishes a radio connection with thebase station. As a result, the network is capable of controlling theuser terminal even when the user terminal performs the D2Dcommunication.

In a first embodiment, another user terminal is provided whichestablishes a radio connection with the base station, the user terminaltransmits the terminal measurement information to the base station, whenthe D2D communication is performed with the other user terminal in astate where a radio connection is established with the base station, andthe network instructs the user terminal to end the D2D communication,when it is determined that interference to the base station exceeds thepermissive amount when the user terminal performs the D2D communicationon the basis of the terminal measurement information. As a result, thenetwork not only controls the start of the D2D communication but alsocontrols the end of the D2D communication, and thus, it is possible tofurther restrain the base station from receiving interference from theD2D communication by the user terminal.

In a first embodiment, the network instructs the user terminal to endthe D2D communication, and instructs the user terminal to performcommunication with the other user terminal by way of the network. As aresult, the network is capable of restraining reception of interferencefrom the user terminal, without ending the communication of the userterminal.

In a second embodiment, the user terminal is capable of transmitting adiscovery-use signal used for discovering a communication partnerterminal in the D2D communication, the base station transmits, to theuser terminal, related information including at least one of:information of a radio resource used when the discovery-use signal istransmitted; and information of a transmission power, and the userterminal transmits the discovery-use signal corresponding to the relatedinformation. As a result, it is possible to restrain the discovery-usesignal transmitted by the user terminal from becoming an interferencesignal to another user terminal existing in the vicinity of the userterminal.

In a third embodiment, when the radio connection between the userterminal and the base station is not established, the user terminaltransmits information indicating establishment of a radio connection inorder to perform only the D2D communication, together with a request forestablishing the radio connection with the base station. As a result, itis possible to omit transmission and reception of information which isnecessary for establishing a normal radio connection and which is notnecessary in the establishment of a radio connection for performing onlythe D2D communication.

In the third embodiment, a mobile communication system that supports D2Dcommunication that is direct device-to-device communication, comprising:three or more user terminals configured to establish a radio connectionwith a base station, wherein the plurality of user terminals eachtransmit, to the base station, terminal measurement informationindicating information obtained by the user terminals each measuring, anetwork including the base station determines, on the basis of theterminal measurement information, whether or not interference to thebase station is smaller than a permissive amount when each of theplurality of user terminals performs the D2D communication, and thenetwork instructs only a user terminal determined to have theinterference to the base station smaller than the permissive amount, outof the plurality of user terminals, to start the D2D communication. As aresult, it is possible to effectively utilize the D2D communication andrestrain the base station from receiving the interference from the D2Dcommunication by the user terminal.

In an embodiment, a base station in a mobile communication system thatsupports D2D communication that is direct device-to-devicecommunication, comprising: a control unit configured to instruct a userterminal to start the D2D communication, when a network including thebase station determines, on the basis of terminal measurementinformation transmitted from the user terminal that establishes a radioconnection with the base station, that interference to the base stationdoes not exceed a permissive amount when the user terminal performs theD2D communication, wherein the terminal measurement informationindicates information obtained by measurement by the user terminal.

In an embodiment, a user terminal in a mobile communication system thatsupports D2D communication that is direct device-to-devicecommunication, comprising: a transmission unit configured to transmit,to a base station, D2D capability information indicating whether theuser terminal has a capability of performing the D2D communication.

In an embodiment, a processor provided in a base station in a mobilecommunication system that supports D2D communication that is directdevice-to-device communication, wherein the processor executes a processof instructing a user terminal to start the D2D communication, when anetwork including the base station determines, on the basis of terminalmeasurement information transmitted from a user terminal thatestablishes a radio connection with the base station, that interferenceto the base station does not exceed a permissive amount when the userterminal performs the D2D communication, and the terminal measurementinformation indicates information obtained by the user terminal.

In an embodiment, a processor provided in a user terminal in a mobilecommunication system that supports D2D communication that is directdevice-to-device communication, wherein the user terminal executes aprocess of transmitting, to a base station, D2D capability informationindicating whether the user terminal has a capability of performing theD2D communication.

Hereinafter, with reference to the accompanying drawings, thedescription will be provided for each embodiment when D2D communicationis introduced to a cellular mobile communication system (hereinafter, an“LTE system”) configured according to the 3GPP standards.

First Embodiment

Hereinafter, the first embodiment will be described.

(LTE System)

FIG. 1 is a configuration diagram of an LTE system according to thepresent embodiment.

As illustrated in FIG. 1, the LTE system includes a plurality of UEs(User Equipments) 100, E-UTRAN (Evolved-Universal Terrestrial RadioAccess Network) 10, and EPC (Evolved Packet Core) 20. The E-UTRAN 10 andthe EPC 20 constitute a network.

The UE 100 is a mobile radio communication device and performs radiocommunication with a cell (a serving cell) with which a connection isestablished. The UE 100 corresponds to the user terminal.

The E-UTRAN 10 includes a plurality of eNBs 200 (evolved Node-Bs). EacheNB 200 corresponds to a base station. The eNB 200 manages a cell andperforms radio communication with the UE 100 that establishes aconnection with the cell.

It is noted that the “cell” is used as a term indicating a minimum unitof a radio communication area, and is also used as a term indicating afunction of performing radio communication with the UE 100.

The eNB 200, for example, has a radio resource management (RRM)function, a function of routing user data, and a measurement controlfunction for mobility control and scheduling.

The EPC 20 includes MME (Mobility Management Entity)/S-GWs(Serving-Gateways) 300, and OAM (Operation and Maintenance) 400.Further, the EPC 20 corresponds to a core network.

The MME is a network node that performs various mobility controls andthe like, for the UE 100 and corresponds to a controller. The S-GW is anetwork node that performs control to transfer user data and correspondsto a mobile switching center.

The eNBs 200 are connected mutually via an X2 interface. Furthermore,the eNB 200 is connected to the MME/S-GW 300 via an S1 interface.

The OAM 400 is a server device managed by an operator and performsmaintenance and monitoring of the E-UTRAN 10.

Next, the configurations of the UE 100 and the eNB 200 will bedescribed.

FIG. 2 is a block diagram of the UE 100. As illustrated in FIG. 2, theUE 100 includes an antenna 101, a radio transceiver 110, a userinterface 120, a GNSS (Global Navigation Satellite System) receiver 130,a battery 140, a memory 150, and a processor 160. The memory 150 and theprocessor 160 constitute a control unit.

The UE 100 may not have the GNSS receiver 130. Furthermore, the memory150 may be integrally formed with the processor 160, and this set (thatis, a chip set) may be called a processor 160′.

The antenna 101 and the radio transceiver 110 are used to transmit andreceive a radio signal. The antenna 101 includes a plurality of antennaelements. The radio transceiver 110 converts a baseband signal outputfrom the processor 160 into the radio signal, and transmits the radiosignal from the antenna 101. Furthermore, the radio transceiver 110converts the radio signal received by the antenna 101 into the basebandsignal, and outputs the baseband signal to the processor 160.

The user interface 120 is an interface with a user carrying the UE 100,and includes, for example, a display, a microphone, a speaker, variousbuttons and the like. The user interface 120 receives an operation froma user and outputs a signal indicating the content of the operation tothe processor 160.

The GNSS receiver 130 receives a GNSS signal in order to obtain locationinformation indicating a geographical location of the UE 100, andoutputs the received signal to the processor 160.

The battery 140 accumulates a power to be supplied to each block of theUE 100.

The memory 150 stores a program to be executed by the processor 160 andinformation to be used for a process by the processor 160.

The processor 160 includes a baseband processor that performs modulationand demodulation, encoding and decoding and the like on the basebandsignal, and a CPU (Central Processing Unit) that performs variousprocesses by executing the program stored in the memory 150. Theprocessor 160 may further include a codec that performs encoding anddecoding on sound and video signals. The processor 160 executes variousprocesses and various communication protocols described later.

FIG. 3 is a block diagram of the eNB 200. As illustrated in FIG. 3, theeNB 200 includes an antenna 201, a radio transceiver 210, a networkinterface 220, a memory 230, and a processor 240. The memory 230 and theprocessor 240 constitute a control unit. In addition, the memory 230 isintegrated with the processor 240, and this set (that is, a chipset) maybe called a processor 240′.

The antenna 201 and the radio transceiver 210 are used to transmit andreceive a radio signal. The antenna 201 includes a plurality of antennaelements. The radio transceiver 210 converts the baseband signal outputfrom the processor 240 into the radio signal, and transmits the radiosignal from the antenna 201. Furthermore, the radio transceiver 210converts the radio signal received by the antenna 201 into the basebandsignal, and outputs the baseband signal to the processor 240.

The network interface 220 is connected to the neighboring eNB 200 viathe X2 interface and is connected to the MME/S-GW 300 via the S1interface. The network interface 220 is used in communication performedon the X2 interface and communication performed on the S1 interface.

The memory 230 stores a program to be executed by the processor 240 andinformation to be used for a process by the processor 240.

The processor 240 includes the baseband processor that performsmodulation and demodulation, encoding and decoding and the like on thebaseband signal and a CPU that performs various processes by executingthe program stored in the memory 230. The processor 240 executes variousprocesses and various communication protocols described later.

FIG. 4 is a protocol stack diagram of a radio interface in the LTEsystem.

As illustrated in FIG. 4, the radio interface protocol is classifiedinto a layer 1 to a layer 3 of an OSI reference model, wherein the layer1 is a physical (PHY) layer. The layer 2 includes a MAC (Media AccessControl) layer, an RLC (Radio Link Control) layer, and a PDCP (PacketData Convergence Protocol) layer. The layer 3 includes an RRC (RadioResource Control) layer.

The PHY layer performs encoding and decoding, modulation anddemodulation, antenna mapping and demapping, and resource mapping anddemapping. The PHY layer provides a transmission service to an upperlayer by using a physical channel. Between the PHY layer of the UE 100and the PHY layer of the eNB 200, data is transmitted through thephysical channel.

The MAC layer performs priority control of data, and a retransmissionprocess and the like by hybrid ARQ (HARQ). Between the MAC layer of theUE 100 and the MAC layer of the eNB 200, data is transmitted via atransport channel. The MAC layer of the eNB 200 includes a transportformat of an uplink and a downlink (a transport block size, a modulationand coding scheme and the like) and a MAC scheduler to decide a resourceblock to be assigned.

The RLC layer transmits data to an RLC layer of a reception side byusing the functions of the MAC layer and the PHY layer. Between the RLClayer of the UE 100 and the RLC layer of the eNB 200, data istransmitted via a logical channel.

The PDCP layer performs header compression and decompression, andencryption and decryption.

The RRC layer is defined only in a control plane. Between the RRC layerof the UE 100 and the RRC layer of the eNB 200, a control signal (an RRCmessage) for various types of setting is transmitted. The RRC layercontrols the logical channel, the transport channel, and the physicalchannel in response to establishment, re-establishment, and release of aradio bearer. When an RRC connection is established between the RRC ofthe UE 100 and the RRC of the eNB 200, the UE 100 is in a connectedstate, and when the RRC connection is not established, the UE 100 is inan idle state.

A NAS (Non-Access Stratum) layer positioned above the RRC layer performssession management and mobility management, for example.

(D2D Communication)

Next, description will be provided by comparing the D2D communicationwith the normal communication (the cellular communication) in the LTEsystem.

FIG. 5 is a diagram illustrating a data path in the cellularcommunication. In this case, FIG. 5 illustrates the case in which thecellular communication is performed between UE 100-1 that establishes aconnection with eNB 200-1 and UE 100-2 that establishes a connectionwith eNB 200-2. It is noted that the data path indicates a transfer pathof user data (a user plane).

As illustrated in FIG. 5, the data path of the cellular communicationpasses through the network. Specifically, the data path is set to passthrough the eNB 200-1, the S-GW 300, and the eNB 200-2.

FIG. 6 is a diagram illustrating a data path in the D2D communication.In this case, FIG. 6 illustrates the case in which the D2D communicationis performed between the UE 100-1 that establishes a connection with theeNB 200-1 and the UE 100-2 that establishes a connection with the eNB200-2.

As illustrated in FIG. 6, the data path of the D2D communication doesnot pass through the network. That is, direct radio communication isperformed between the UEs. As described above, when the UE 100-2 existsin the vicinity of the UE 100-1, the D2D communication is performedbetween the UE 100-1 and the UE 100-2, thereby obtaining an effect thata traffic load of the network and a battery consumption amount of the UE100 are reduced, for example. In addition, in a mode called LocallyRouted (locally routed mode), a data path passes through the eNB 200without passing through the S-GW 300.

It is noted that cases in which the D2D communication is started include(a) a case in which the D2D communication is started after a partnerterminal is discovered by performing an operation for discovering apartner terminal (a proximal terminal), and (b) a case in which the D2Dcommunication is started without performing an operation for discoveringa partner terminal (a proximal terminal).

For example, in the above-described case (a), one UE 100 of the UE 100-1and the UE 100-2 discovers the other UE 100 existing in the proximity ofthe one UE 100, so that the D2D communication is started.

In such a case, in order to discover a partner terminal, the UE 100 hasa (Discover) function of discovering another UE (a proximal terminal)100 existing in the proximity of the UE 100, and/or a (Discoverable)function of being discovered by another UE 100.

Specifically, the UE 100-1 transmits a discovery signal (Discoverysignal/Discoverable signal) that is used to either discover a partnerterminal (a proximal terminal) or to be discovered by a partner terminal(a proximal terminal). The UE 100-2 having received the discovery signaldiscovers the UE 100-1. When the UE 100-2 transmits a response to thediscovery signal, the UE 100-1 having transmitted the discovery signaldiscovers the UE 100-2, which is the partner terminal.

It is noted that the UE 100 need not necessarily perform the D2Dcommunication even upon discovering a partner terminal, for example,after mutually discovering each other, the UE 100-1 and the UE 100-2 mayperform a negotiation, and determine whether or not to perform the D2Dcommunication. When each of the UE 100-1 and the UE 100-2 agrees toperform the D2D communication, the D2D communication starts. It is notedthat when the UE 100-1 does not perform the D2D communication afterdiscovering a partner terminal, the UE 100-1 may report, to an upperlayer (for example, an application), the discovery of the proximal UE100 (that is, the UE 100-2). For example, the application is capable ofexecuting a process based on the report (for example, a process ofplotting the position of the UE 100-2 in the geographical information).

Moreover, the UE 100 is capable of reporting the discovery of a proximalterminal to the eNB 200, and is also capable of receiving, from the eNB200, an instruction regarding whether to communicate with the partnerterminal through the cellular communication or through the D2Dcommunication.

On the other hand, in the above-described case (b), for example, the UE100-1 starts the transmission (such as a notification throughbroadcasting) of a signal for the D2D communication without specifying apartner terminal. Thus, the UE 100 is capable of starting the D2Dcommunication regardless of the existence of the discovery of a partnerterminal. It is noted that the UE 100-2 that is performing the standbyoperation for the signal for the D2D communication performssynchronization or/and demodulation on the basis of the signal from theUE 100-1.

(Operation of Mobile Communication System According to First Embodiment)

Next, an operation of a mobile communication system according to a firstembodiment will be described with reference to FIG. 7 to FIG. 9B. FIG. 7is a diagram for explaining the operation of the mobile communicationsystem according to the first embodiment. FIG. 8 is a sequence diagramillustrating an operation example of the mobile communication systemaccording to the first embodiment.

As shown in FIG. 7, the UE 100-1 and the UE 100-2 exist in a cell 250managed by the eNB 200. Further, as shown in FIG. 7 and FIG. 8, each ofthe UE 100-1 and the UE 100-2 establishes a connection with the eNB 200,and the UE 100-1 and the UE 100-2 perform cellular communication passingthrough a core network.

As shown in FIG. 8, in step 101, the UE 100-1 transmits D2D supportinformation indicating whether the UE 100-1 supports the D2Dcommunication, to the eNB 200. Likewise, the UE 100-2 transmits the D2Dsupport information to the eNB 200. The eNB 200 receives the D2D supportinformation.

Examples of the D2D support information include: (a) informationindicating that the UE 100 supports the D2D communication using anuplink and a downlink in all the bands supporting the cellularcommunication (D2D capability); (b) information indicating that the UE100 supports the D2D communication using the uplink and/or the downlinkin all the bands supporting the cellular communication (D2D capabilityper UL/DL); (c) information indicating that the UE 100 supports the D2Dcommunication using the uplink and the downlink in a predetermined band(D2D capability per band); (d) information indicating that the UE 100supports the D2D communication using the uplink and/or the downlink in apredetermined band (D2D capability per band +UL/DL); and (e) informationindicating that the UE 100 supports the D2D communication using theuplink and/or the downlink in a predetermined band of the uplink and/ora predetermined band of the downlink (D2D capability per UL/DL perband).

The D2D support information may be notified to the eNB 200 by using theUE Capability Information. For the D2D support information, a new FGIbit may be defined. Further, the D2D support information may be includedin UE EUTRA Capability.

In step 102, the eNB 200 determines whether each of the UE 100-1 and theUE 100-2 supports the D2D communication. Specifically, the eNB 200determines, on the basis of the D2D support information, whether or noteach of the UE 100-1 and the UE 100-2 supports the D2D communication, ina band ensured by the eNB 200 for the D2D communication in the uplinkand/or the downlink.

In step 103, the eNB 200 requests the terminal measurement informationto each of the UE 100-1 and the UE 100-2. Each of the UE 100-1 and theUE 100-2 receives a terminal measurement information request. Theterminal measurement information will be described in detail later.

Further, in the present embodiment, the eNB 200 requests the terminalmeasurement information, and requests that the UE 100-1 and the UE 100-2implement Discovery.

Further, in the present embodiment, the eNB 200 requests the terminalmeasurement information, and transmits the confirmation information.Each of the UE 100-1 and the UE 100-2 receives the confirmationinformation.

The confirmation information is information for confirming the UE 100whether or not to consent to perform the D2D communication. Whenreceiving the confirmation information, each of the UE 100-1 and the UE100-2 may display information indicating whether to consent to performthe D2D communication on a display included in a user interface 120.

In step 104, each of the UE 100-1 and the UE 100-2 implementsmeasurement. Specifically, each of the UE 100-1 and the UE 100-2measures at least one of a location and a radio environment.

When measuring the radio environment, the UE 100-1 measures a receivedpower intensity (for example, RSRP) and/or reception quality (forexample, RSRQ) of a signal received from the eNB 200. Further, the UE100-1 measures the received power intensity and/or reception quality ofa signal received from the UE 100-2, that is a partner terminal.Similarly to the UE 100-1, the UE 100-2 measures the radio environment.

In step 105, the UE 100-1 and the UE 100-2 implement Discovery. Forexample the UE 100-1 transmits a discovery-use signal used fordiscovering a communication partner terminal in the D2D communication(hereinafter, referred to as “Discovery signal”) . When receiving theDiscovery signal, the UE 100-2 transmits a response signal for theDiscovery signal (Discovery response signal), to the UE 100-1. The UE100-1 receives the Discovery response signal.

In step 106, each of the UE 100-1 and the UE 100-2 transmits theterminal measurement information. The eNB 200 receives the terminalmeasurement information.

The terminal measurement information indicates information obtained bymeasurement by the UE 100. Specifically, the terminal measurementinformation is information obtained by the measurement in theabove-described step 104, and examples thereof include at least one oflocation information indicating the location of the UE 100 (detailedlocation information) and radio environment information indicting theradio environment of the UE 100.

The UE 100-1 transmits, as the terminal measurement information, theinformation measured in step 104. Further, the UE 100-1 may transmit, asthe terminal measurement information, information (for example, pathlossinformation) obtained on the basis of the information measured in step104. Similarly to the UE 100-1, the UE 100-2 transmits the terminalmeasurement information.

It is noted that the pathloss information is obtained by a differencebetween transmission power intensity included in a reference signal anda received power intensity of the reference signal, for example.

Each of the UE 100-1 and the UE 100-2 may regularly transmit theterminal measurement information in accordance with an instruction fromthe eNB 200. Alternatively, each of the UE 100-1 and the UE 100-2 maytransmit the terminal measurement information by using a predeterminedevent, as a trigger, designated from the eNB 200. In the presentembodiment, each of the UE 100-1 and the UE 100-2 transmits the terminalmeasurement information by using a request for the terminal measurementinformation, as a trigger.

In the present embodiment, each of the UE 100-1 and the UE 100-2transmits, together with the terminal measurement information, D2Dterminal discovery information. The eNB 200 receives the D2D terminaldiscovery information.

The D2D terminal discovery information is information indicating thatthe communication partner terminal in the D2D communication isdiscovered or cannot be discovered.

In the present embodiment, the UE 100-1 receives the Discovery responsesignal and the UE 100-2 receives the Discovery signal, and thus, each ofthe UE 100-1 and the UE 100-2 transmits, as the D2D terminal discoveryinformation, information indicating that the communication partnerterminal in the D2D communication is discovered.

It is noted that when the Discovery signal is transmitted and theDiscovery response signal is not received for a predetermined timeperiod, the UE 100-1 transmits information indicating that thecommunication partner terminal cannot be discovered. Further, when theDiscovery signal is no received for a predetermined time period, the UE100-2 transmits information indicating that the communication partnerterminal cannot be discovered.

Further, each of the UE 100-1 and the UE 100-2 transmits the terminalmeasurement information, and transmits consent information indicatingwhether to consent to that the D2D communication is performed, to theeNB 200. Each of the UE 100-1 and the UE 100-2 may transmit the consentinformation to the eNB 200, only when the confirmation information isreceived from the eNB 200.

In step 107, the eNB 200 determines whether the UE 100-1 and the UE100-2 are caused to perform the D2D communication. In the presentembodiment, the eNB 200 performs (1) determination based on the terminalmeasurement information, (2) determination based on the D2D terminaldiscovery information, (3) determination based on the consentinformation, and (4) final determination.

(1) Determination Based on Terminal Measurement Information

The eNB 200 determines, on the basis of the terminal measurementinformation, whether the interference to the eNB 200 does not exceed thepermissive amount, when each of the UE 100-1 and the UE 100-2 performsthe D2D communication. A specific determination method will be describedwith reference to FIG. 9A and FIG. 9B.

FIG. 9A is a diagram for explaining a distance between the eNB 200; andthe UE 100-1 and the UE 100-2. FIG. 9B is a diagram for explainingreceived power intensity and reception quality of a signal received byeach of the eNB 200, the UE 100-1, and the UE 100-2.

The eNB 200 is capable of making a determination by the followingdetermination methods, depending on a content of the terminalmeasurement information received from each of the UE 100-1 and the UE100-2.

(A) Determination Method Based on Location Information

(A1) Determination Method A1

When receiving the location information of the UE 100-1, the eNB 200evaluates a distance X1 from the eNB 200 to the UE 100-1 on the basis ofthe location information of the eNB 200 and the location information ofthe UE 100-1.

The eNB 200 determines, on the basis of the distance X1, whether theinterference from the UE 100-1 to the eNB 200 does not exceed thepermissive amount. Specifically, when the distance X1 is equal to ormore than a predetermined value, the eNB 200 determines that theinterference from the UE 100-1 to the eNB 200 does not exceed thepermissive amount, and when the distance X1 is less than thepredetermined value, the eNB 200 determines that the interference fromthe UE 100-1 to the eNB 200 exceeds the permissive amount.

Further, when receiving the location information of the UE 100-2, theeNB 200 evaluates a distance X2 from the eNB 200 to the UE 100-2.Similarly to the above, the eNB 200 determines whether the interferencefrom the UE 100-2 to the eNB 200 does not exceed the permissive amount.

(A2) Determination Method A2

When receiving the location information of each of the UE 100-1 and theUE 100-2, the eNB 200 evaluates a distance X3 from the UE 100-1 to theUE 100-2, in addition to the distance X1 and the distance X2.

The eNB 200 determines, on the basis of the distance X1 and the distanceX3, whether the interference from the UE 100-1 to the eNB 200 does notexceed the permissive amount. Specifically, when the distance X1 isequal to or more than a value obtained by adding an offset value to thedistance X3 (that is, when X1≧X3+offset value is satisfied), the eNB 200determines that the interference from the UE 100-1 to the eNB 200 doesnot exceed the permissive amount, and when the distance X1 is less thana value obtained by adding an offset value to the distance X3 (that is,when X1<X3+offset value is satisfied), the eNB 200 determines that theinterference from the UE 100-1 to the eNB 200 exceeds the permissiveamount.

Further, similarly to the above, when the distance X2 is equal to ormore than a value obtained by adding an offset value to the distance X3(that is, when X2≧X3+offset value is satisfied), the eNB 200 determinesthat the interference from the UE 100-2 to the eNB 200 does not exceedthe permissive amount, and when the distance X2 is less than a valueobtained by adding an offset value to the distance X3 (that is, whenX2<X3+offset value is satisfied), the eNB 200 determines that theinterference from the UE 100-2 to the eNB 200 exceeds the permissiveamount.

(B) Determination Method Based on Received Power Intensity

(B1) Determination Method B1

When receiving information indicating a received power intensity Pe1 ofthe signal received by the UE 100-1 from the eNB 200, the eNB 200determines, on the basis of the received power intensity Pe1, whetherthe interference from the UE 100-1 to the eNB 200 does not exceed thepermissive amount.

Specifically, when the received power intensity Pe1 is smaller than apredetermined value, the eNB 200 determines that the interference fromthe UE 100-1 to the eNB 200 does not exceed the permissive amount, andwhen the received power intensity Pe1 is equal to or more than thepredetermined value, the eNB 200 determines that the interference fromthe UE 100-1 to the eNB 200 exceeds the permissive amount.

Further, when receiving information indicating a received powerintensity Pet of the signal received by the UE 100-2 from the eNB 200,the eNB 200 determines, similarly to the above, whether the interferencefrom the UE 100-2 to the eNB 200 does not exceed the permissive amount.

(B2) Determination Method B2

When receiving information indicating a received power intensity Pu1 ofthe signal received by the UE 100-2 from the UE 100-1, the eNB 200determines, on the basis of the received power intensity Pu1 and areceived power intensity Pa of the signal received by the eNB 200 fromthe UE 100-1, whether the interference from the UE 100-1 to the eNB 200does not exceed the permissive amount.

Specifically, when the received power intensity Pa is equal to or morethan a value obtained by adding an offset value to the received powerintensity Pu1 (that is, when Pa≧Pu1+offset value is satisfied), the eNB200 determines that the interference from the UE 100-1 to the eNB 200does not exceed the permissive amount, and when the received powerintensity Pa is less than a value obtained by adding an offset value tothe received power intensity Pu1 (that is, when Pa<Pu1+offset value issatisfied), the eNB 200 determines that the interference from the UE100-1 to the eNB 200 exceeds the permissive amount.

Further, when receiving the received power intensity Pu2 of the signalreceived by the UE 100-1 from the UE 100-2, similarly to the above, theeNB 200 determines, on the basis of the received power intensity Pu2 anda received power intensity Pb of the signal received by the eNB 200 fromthe UE 100-1, whether the interference from the UE 100-2 to the eNB 200does not exceed the permissive amount.

(C) Determination Method Based on Reception Quality

(C1) Determination Method C1

When receiving information indicating reception quality Qe1 of thesignal received by the UE 100-1 from the eNB 200, the eNB 200determines, on the basis of the reception quality Qe1, whether theinterference from the UE 100-1 to the eNB 200 does not exceed thepermissive amount.

Specifically, when the reception quality Qe1 is smaller than apredetermined value, the eNB 200 determines that the interference fromthe UE 100-1 to the eNB 200 does not exceed the permissive amount, andwhen the reception quality Qe1 is equal to or more than thepredetermined value, the eNB 200 determines that the interference fromthe UE 100-1 to the eNB 200 exceeds the permissive amount.

Further, when receiving information indicating reception quality Qe2 ofthe signal received by the UE 100-2 from the eNB 200, the eNB 200determines, similarly to the above, whether the interference from the UE100-2 to the eNB 200 does not exceed the permissive amount.

(C2) Determination Method C2

When receiving information indicating reception quality Qu1 of thesignal received by the UE 100-2 from the UE 100-1, the eNB 200determines, on the basis of the reception quality Qu1 and receptionquality of the signal received by the eNB 200 from the UE 100-1, whetherthe interference from the UE 100-1 to the eNB 200 does not exceed thepermissive amount.

Specifically, when the reception quality Qa is equal to or more than avalue obtained by adding an offset value to the reception quality Qu1(that is, when Qa≧Qu1+offset value is satisfied), the eNB 200 determinesthat the interference from the UE 100-1 to the eNB 200 does not exceedthe permissive amount, and when the reception quality Qa is less than avalue obtained by adding an offset value to the reception quality Qu1(that is, when Qa<Qu1+offset value is satisfied), the eNB 200 determinesthat the interference from the UE 100-1 to the eNB 200 exceeds thepermissive amount.

Further, when receiving reception quality Qu2 of the signal received bythe UE 100-1 from the UE 100-2, the eNB 200 determines, similarly to theabove, on the basis of the reception quality Qu2 and reception qualityQb of the signal received by the eNB 200 from the UE 100-1 whether theinterference from the UE 100-2 to the eNB 200 does not exceed thepermissive amount.

(D) Determination Method Based on Pathloss

(D1) Determination Method D1

When receiving pathloss information between the eNB 200 and the UE100-1, the eNB 200 determines, on the basis of the pathloss information,whether the interference from the UE 100-1 to the eNB 200 does notexceed the permissive amount.

It is noted that when receiving the information indicating the receivedpower intensity Pe1 of the signal received by the UE 100-1 from the eNB200, the eNB 200 may use a pathloss calculated from a difference betweenthe transmission power intensity of the signal transmitted by the eNB200 and the received power intensity Pe1.

Specifically, when the pathloss between the eNB 200 and the UE 100-1 isgreater than a predetermined value, the eNB 200 determines that theinterference from the UE 100-1 to the eNB 200 does not exceed thepermissive amount, and when the received power intensity Pe1 is equal toor more than the predetermined value, the eNB 200 determines that theinterference from the UE 100-1 to the eNB 200 exceeds the permissiveamount.

Further, when receiving pathloss information between the eNB 200 and theUE 100-2, similarly to the above, the eNB 200 determines, on the basisof the pathloss information, whether the interference from the UE 100-2to the eNB 200 does not exceed the permissive amount.

It is noted that when receiving the information indicating the receivedpower intensity Pe2 of the signal received by the UE 100-2 from the eNB200, the eNB 200 may use a calculated pathloss, similarly to the above.

(D2) Determination Method D2

When receiving the pathloss information between the UE 100-1 and the UE100-2, the eNB 200 determines, on the basis of a pathloss PLu betweenthe UE 100-1 and the UE 100-2 and a pathloss PLe1 between the eNB 200and the UE 100-1, whether the interference from the UE 100-1 to the eNB200 does not exceed the permissive amount.

Specifically, when the pathloss PLe1 is equal to or more than a valueobtained by adding an offset value to the pathloss PLu (that is, whenPLe1≧PLu+offset value is satisfied), the eNB 200 determines that theinterference from the UE 100-1 to the eNB 200 does not exceed thepermissive amount, and when the pathloss PLe1 is less than a valueobtained by adding an offset value to the pathloss PLu (that is, whenPLe1<PLu+offset value is satisfied), the eNB 200 determines that theinterference from the UE 100-1 to the eNB 200 exceeds the permissiveamount.

Further, similarly to the above, the eNB 200 determines, on the basis ofthe pathloss PLu between the UE 100-1 and the UE 100-2 and the pathlossPLe2 between the eNB 200 and the UE 100-2, whether the interference fromthe UE 100-1 to the eNB 200 does not exceed the permissive amount.

It is noted that when the eNB 200 determines whether the interferencefrom the UE 100-1 to the eNB 200 does not exceed the permissive amount,it is preferable that a pathloss of the signal transmitted from the UE100-1 to the UE 100-2 is used as the pathloss PLu between the UE 100-1and the UE 100-2. Further, when the eNB 200 determines whether theinterference from the UE 100-2 to the eNB 200 does not exceed thepermissive amount, it is preferable that a pathloss of the signaltransmitted from the UE 100-2 to the UE 100-1 is used as the pathlossPLu between the UE 100-1 and the UE 100-2.

When each of the UE 100-1 and the UE 100-2 performs the D2Dcommunication by using at least one of the above-described determinationmethods, the eNB 200 determines whether the interference to the eNB 200does not exceed the permissive amount.

When determining that the interference to the eNB 200 when the UE 100-1and the UE 100-2 perform the D2D communication does not exceed thepermissive amount, the eNB 200 determines that the UE 100-1 and the UE100-2 are caused to perform the D2D communication. On the other hand,when determining that the interference to the eNB 200 when the UE 100-1and the UE 100-2 perform the D2D communication exceeds the permissiveamount, the eNB 200 determines that the UE 100-1 and the UE 100-2 arenot caused to perform the D2D communication.

(2) Determination Based on D2D Terminal Discovery Information

Further, in the present embodiment, the eNB 200 determines, on the basisof the D2D terminal discovery information, whether the UE 100-1 and theUE 100-2 are caused to perform the D2D communication.

When at least one of the UE 100-1 and the UE 100-2 already discovers thecommunication partner terminal, the eNB 200 determines that the UE 100-1and the UE 100-2 are caused to perform the D2D communication. On theother hand, when the UE 100-1 and the UE 100-2 do not discover thecommunication partner terminal, the eNB 200 determines that the UE 100-1and the UE 100-2 are not caused to perform the D2D communication.

It is noted that in the present embodiment, the eNB 200 receives theinformation indicating that the communication partner terminal in theD2D communication is discovered, and thus, the eNB 200 determines thatthe UE 100-1 and the UE 100-2 are caused to perform the D2Dcommunication.

(3) Determination Based on Consent Information

Further, in the present embodiment, the eNB 200 determines, on the basisof the consent information, whether the UE 100-1 and the UE 100-2 arecaused to perform the D2D communication.

When each of the UE 100-1 and the UE 100-2 transmits the informationindicating that each of the UE 100-1 and the UE 100-2 consents to theD2D communication, the eNB 200 determines that the UE 100-1 and the UE100-2 are caused to perform the D2D communication. On the other hand,when each of the UE 100-1 and the UE 100-2 transmits the informationindicating that at least one of the UE 100-1 and the UE 100-2 does notconsent to the D2D communication, the eNB 200 determines that the UE100-1 and the UE 100-2 are not caused to perform the D2D communication.

(4) Final Determination

When determining that the UE 100-1 and the UE 100-2 are caused toperform the D2D communication, the eNB 200 finally executes a process instep 108. Specifically, when determining that the UE 100-1 and the UE100-2 are caused to perform the D2D communication in all of theabove-described determinations (1) to (3), the eNB 200 executes theprocess in step 108.

In step 108, the eNB 200 instructs each of the UE 100-1 and the UE 100-2to start the D2D communication. Each of the UE 100-1 and the UE 100-2receives the instruction to start the D2D communication.

In the present embodiment, although not receiving the request for theD2D communication from each of the UE 100-1 and the UE 100-2, the eNB200 instructs the start of the D2D communication. That is, when it isdetermined that the interference from each of the UE 100-1 and the UE100-2 to the eNB 200 is smaller than the permissive amount and when theUE 100-1 and the UE 100-2 perform communication by way of the network,the eNB 200 instructs the start of the D2D communication even when thereis no request for the D2D communication from each of the UE 100-1 andthe UE 100-2. When each of the UE 100-1 and the UE 100-2 alreadyconsents to perform the D2D communication, the eNB 200 may instruct thestart of the D2D communication.

It is noted that the eNB 200 may transmit, in addition to theinstruction to start the D2D communication, information necessary forperforming the D2D communication (for example, scheduling informationindicating a radio resource assigned to the D2D communication betweenthe UE 100-1 and the UE 100-2.

In step 109, the UE 100-1 and the UE 100-2 perform the D2Dcommunication.

It is noted that the UE 100-1 and the UE 100-2 that receive theinstruction to start the D2D communication perform negotiation ofinformation used for establishing a D2D link. Information that is usedfor establishing the D2D link is the scheduling information, forexample.

When the D2D link is established between the UE 100-1 and the UE 100-2,the UE 100-1 reports to the eNB 200-2 that the D2D link is established.The reported eNB 200-2 ends the cellular communication performed by theUE 100-1 and the UE 100-2.

(Operation of Mobile Communication System According to Modification ofFirst Embodiment)

Next, with reference to FIG. 10, an operation of a mobile communicationsystem according to a modification of the first embodiment will bedescribed. It is noted that description will proceed on the basis mainlyof a portion different from the above-described embodiment, and asimilar portion will not be described, where necessary.

In the above-described first embodiment, a case where the UE 100-1 andthe UE 100-2 start the D2D communication is described. In the presentmodification, a case where the UE 100-1 and the UE 100-2 end the D2Dcommunication will be described.

FIG. 10 is a sequence diagram showing an operation example of the mobilecommunication system according to the modification of the firstembodiment.

As shown in FIG. 10, each of the UE 100-1 and the UE 100-2 establishes aconnection with the eNB 200, and the UE 100-1 and the UE 100-2 performthe D2D communication.

As shown in FIG. 10, in step 201, the eNB 200 requests the terminalmeasurement information to each of the UE 100-1 and the UE 100-2. Eachof the UE 100-1 and the UE 100-2 receives the request for the terminalmeasurement information.

In step 202, each of the UE 100-1 and the UE 100-2 implements themeasurement on the basis of the request for the terminal measurementinformation from the eNB 200.

In step 203, each of the UE 100-1 and the UE 100-2 transmits theterminal measurement information. The eNB 200 receives the terminalmeasurement information.

In step 204, the eNB 200 determines whether or not the UE 100-1 and theUE 100-2 are caused to end the D2D communication. That is, the eNB 200determines whether or not the UE 100-1 and the UE 100-2 are caused tocontinue the D2D communication.

The eNB 200 determines, on the basis of the terminal measurementinformation, whether the interference to the eNB 200 does not exceed thepermissive amount, when each of the UE 100-1 and the UE 100-2 isperforming the D2D communication.

The eNB 200 determines whether the interference to the eNB 200 does notexceed the permissive amount according to the determination methodsimilar to that in step 107 in the first embodiment.

When at least either one of the UE 100-1 or the UE 100-2 performs theD2D communication, if the eNB 200 determines that the interference tothe eNB 200 exceeds the permissive amount, then a process in step 205 isexecuted.

When determining that the interference to the eNB 200 does not exceedthe permissive amount when the UE 100-1 and the UE 100-2 perform the D2Dcommunication, the eNB 200 may again execute the process in step 205.

In step 205, the eNB 200 instructs each of the UE 100-1 and the UE 100-2to end the D2D communication. Each of the UE 100-1 and the UE 100-2receives the instruction to end the D2D communication.

The eNB 200 instructs the end of the D2D communication, and gives aninstruction to the UE 100-1 that the UE 100-1 communicates with the UE100-2 byway of the eNB 200. Further, similarly, the eNB 200 instructsthe end of the D2D communication, and gives an instruction to the UE100-2 that the UE 100-2 communicates with the UE 100-1 by way of the eNB200.

The eNB 200 releases the frequency band assigned to the D2Dcommunication between the UE 100-1 and the UE 100-2, and forcedly stopsthe D2D communication.

In step 206, the UE 100-1 and the UE 100-2 perform the cellularcommunication.

(Summary of First Embodiment)

In the present embodiment, each of the UE 100-1 and the UE 100-2transmits the terminal measurement information to the eNB 200, and whendetermining on the basis of the terminal measurement information thatthe interference to the eNB 200 does not exceed the permissive amountwhen each of the UE 100-1 and the UE 100-2 performs the D2Dcommunication, the eNB 200 instructs each of the UE 100-1 and the UE100-2 to start the D2D communication. As a result, when the eNB 200determines that the interference to the eNB 200 exceeds the permissiveamount when the UE 100-1 and the UE 100-2 perform the D2D communication,the UE 100-1 and the UE 100-2 does not start the D2D communication, andtherefore, it is possible to restrain the eNB 200 from receivinginterference from the D2D communication by the UE 100-1 and the UE100-2.

In the present embodiment, the terminal measurement information is thelocation information, and the eNB 200 determines whether theinterference to the eNB 200 does not exceed the permissive amount, onthe basis of the distance, between the eNB 200 and the UE 100, evaluatedfrom the location information. As a result, the eNB 200 is capable ofmaking a determination irrespective of an accidental change in radioenvironment in the eNB 200 or the UE 100, and thus, it is possible tomake a stable determination.

In the present embodiment, the terminal measurement information is theradio environment information, and the eNB 200 determines whether theinterference to the eNB 200 does not exceed the permissive amount, onthe basis at least one of the received power intensity that is evaluatedfrom the radio environment information and that is received by the UE100, and the pathloss between the eNB 200 and the UE 100. As a result,the eNB 200 is capable of making a determination on the basis of anactual radio environment of the UE 100, and thus, it is possible toimprove the accuracy in the determination.

In the present embodiment, the UE 100 transmits the D2D supportinformation, and on the basis of the D2D support information, the eNB200 determines whether or not the UE 100 supports the D2D communication.As a result, it is possible for the eNB 200 to eliminate a need ofrequesting unnecessary terminal measurement information for determiningwhether the D2D communication is to be performed, to the UE 100 thatdoes not support the D2D communication.

In the present embodiment, when it is determined that the interferencefrom each of the UE 100-1 and the UE 100-2 to the eNB 200 is smallerthan the permissive amount and when the UE 100-1 and the UE 100-2perform communication by way of the network, the eNB 200 instructs thestart of the D2D communication even when there is no request for the D2Dcommunication from each of the UE 100-1 and the UE 100-2. As a result,the UE 100-1 and the UE 100-2 perform the D2D communication, and thus,it is possible to reduce a load of traffic at the eNB 200.

In the present embodiment, the eNB 200 transmits the confirmationinformation for confirming whether or not to consent to perform the D2Dcommunication, to each of the UE 100-1 and the UE 100-2, and whenreceiving the consent to performing the D2D communication from each ofthe UE 100-1 and the UE 100-2, the eNB 200 instructs the UE 100-1 andthe UE 100-2 to start the D2D communication. As a result, it is possibleto restrain the eNB 200 from forcedly causing the UE 100-1 and the UE100-2 to perform the D2D communication against the intention of eachuser using each of the UE 100-1 and the UE 100-2.

In the present embodiment, when the D2D communication is performed onlyin a state where each of the UE 100-1 and the UE 100-2 establishes theradio connection with the eNB 200, the eNB 200 may instruct each of theUE 100-1 and the UE 100-2 to start the D2D communication. As a result,even when the UE 100-1 and the UE 100-2 perform the D2D communication,the eNB 200 is capable of controlling the UE 100-1 and the UE 100-2.

In the present embodiment, when the D2D communication is performed in astate where the radio connection is established with the eNB 200, eachof the UE 100-1 and the UE 100-2 transmits the terminal measurementinformation to the eNB 200, and when the eNB 200 determines on the basisof the terminal measurement information that the interference to the eNB200 exceeds the permissive amount when the UE 100-1 and the UE 100-2perform the D2D communication, the eNB 200 instructs each of the UE100-1 and the UE 100-2 to end the D2D communication. As a result, theeNB 200 not only controls the start of the D2D communication but alsocontrols the end of the D2D communication, and thus, it is possible tofurther restrain the eNB 200 from receiving interference from the D2Dcommunication by the UE 100-1 and the UE 100-2.

In the present embodiment, the eNB 200 instructs the UE 100-1 and the UE100-2 to end the D2D communication, and instructs the UE 100-1 and theUE 100-2 to perform the communication by way of the eNB 200. As aresult, the eNB 200 is capable of restraining reception of interferencefrom the UE 100-1 and the UE 100-2, without ending the communication ofthe UE 100-1 and the UE 100-2.

Second Embodiment

(Operation of Mobile Communication System According to SecondEmbodiment)

Next, with reference to FIG. 11, an operation of a mobile communicationsystem according to a second embodiment will be described. It is notedthat description will proceed on the basis mainly of a portion differentfrom the above-described embodiment and modification, and a similarportion will not be described, where necessary

In the above-described first embodiment, a case is described where eachof the UE 100-1 and the UE 100-2 does not give a request for the D2Dcommunication, to the eNB 200. In the present embodiment, however, acase is described where each of the UE 100-1 and the UE 100-2 gives arequest for the D2D communication to the eNB 200.

FIG. 11 is a sequence diagram showing an operation example of the mobilecommunication system according to the second embodiment.

As shown in FIG. 11, each of the UE 100-1 and the UE 100-2 establishes aconnection with the eNB 200.

As shown in FIG. 11, in step 301, the eNB 200 transmits Discoveryrelated information including information of the radio resource usedwhen the Discovery signal is transmitted and/or information of thetransmission power, to the UE 100-1 and the UE 100-2. Each of the UE100-1 and the UE 100-2 receives the Discovery related information.

The Discovery related information is information including theinformation of the radio resource used when the Discovery signal istransmitted and/or the information of the transmission power. Theinformation of the radio resource used when the Discovery signal istransmitted includes at least one item of information of a time resourceand information of a frequency resource. It is noted that the eNB 200-1selects the radio resource and the transmission power by which theDiscovery signal will not act as an interference signal to the UE 100connected to the cell 250 or/and the cell managed by a neighboring basestation, and includes the selected radio resource and the transmissionpower into the Discovery related information.

In the present embodiment, the eNB 200 transmits the Discovery relatedinformation by broadcast. For example, the eNB 200 transmits theDiscovery related information into a system information block (SIB).When the Discovery related information is included in the systeminformation block (SIB), each of the UE 100-1 and the UE 100-2 iscapable of receiving the Discovery related information even in an idlestate. It is noted that the eNB 200 may transmit the Discovery relatedinformation by unicast.

In step 302, the UE 100-1 and the UE 100-2 implement the Discovery.

In the present embodiment, each of the UE 100-1 and the UE 100-2transmits the Discovery signal corresponding to the Discovery relatedinformation. Specifically, the UE 100-1 (or the UE 100-2) decides theradio resource and the transmission power used when the Discovery signalis transmitted, on the basis of the information of the radio resourceand/or the information of the transmission power included in theDiscovery related information. Each of the UE 100-1 and the UE 100-2starts transmitting the Discovery signal on the basis of the decidedradio resource and transmission power.

In step 303, each of the UE 100-1 and the UE 100-2 transmits the requestfor the D2D communication and the D2D terminal discovery information.The eNB 200 receives the request for the D2D communication and the D2Dterminal discovery information.

In step 304, each of the UE 100-1 and the UE 100-2 implementsmeasurement.

In step 305, each of the UE 100-1 and the UE 100-2 transmits theterminal measurement information. The eNB 200 receives the terminalmeasurement information.

Further, in step 306, the eNB 200 determines, on the basis of theterminal measurement information, whether the UE 100-1 and the UE 100-2are caused to perform the D2D communication.

In the present embodiment, description proceeds with an assumption of acase where when the UE 100-1 and the UE 100-2 perform the D2Dcommunication, the eNB 200 is not capable of determining that theinterference to the eNB 200 does not exceed the permissive amount.Examples of the case include: when the eNB 200 makes a determinationaccording to a plurality of determination methods, determination resultsdisagree depending on each determination method. Another case includes:although it is determined that the interference to the eNB 200, when oneUE 100 (for example, the UE 100-1) performs the D2D communication, doesnot exceed the permissive amount, it is determined that the interferenceto the eNB 200 when the other UE 100 (for example, the UE 100-2)performs the D2D communication exceeds the permissive amount.

In step 307, the eNB 200 requests each of the UE 100-1 and the UE 100-2that has transmitted the terminal measurement information to transmitthe terminal measurement information. Each of the UE 100-1 and the UE100-2 receives the request for the terminal measurement information.

The eNB 200 may explicitly request to transmit terminal measurementinformation (hereinafter, referred to as “new terminal measurementinformation”) different from the terminal measurement informationalready transmitted by the UE 100 (hereinafter, referred to as “oldterminal measurement information”).

The new terminal measurement information may be information different intype from the old terminal measurement information, and may beinformation measured later than the time when the old terminalmeasurement information was measured.

In step 308, each of the UE 100-1 and the UE 100-2 implementsmeasurement.

Each of the UE 100-1 and the UE 100-2 implements the measurement,triggered by the request for the terminal measurement information.

It is noted that when each of the UE 100-1 and the UE 100-2 performs themeasurement after transmitting the old terminal measurement informationto the eNB 200 and before receiving the request for the terminalmeasurement information, each of the UE 100-1 and the UE 100-2 iscapable of transmitting the information acquired by the measurement asthe new terminal measurement information, to the eNB 200, and thus, itis possible to omit the process in step 308.

In step 309, each of the UE 100-1 and the UE 100-2 transmits theterminal measurement information (new terminal measurement information).The eNB 200 receives the terminal measurement information.

In step 310, the eNB 200 determines, on the basis of the terminalmeasurement information (new terminal measurement information), whetherthe UE 100-1 and the UE 100-2 are caused to perform the D2Dcommunication.

When determining on the basis of the new terminal measurementinformation that the interference to the eNB 200 does not exceed thepermissive amount when the UE 100-1 and the UE 100-2 perform the D2Dcommunication, the eNB 200 executes a process in step 311.

Step 311 and step 312 correspond to step 108 and step 109 in the firstembodiment, respectively.

(Summary of Second Embodiment)

In the present embodiment, the eNB 200 transmits the Discovery relatedinformation including the information of the radio resource used whenthe Discovery signal is transmitted and/or the information of thetransmission power, to the UE 100-1 and the UE 100-2, and the UE 100-1transmits the Discovery signal corresponding to the Discovery relatedinformation. As a result, it is possible to restrain the Discoverysignal transmitted by the UE 100-1 from becoming an interference signalto another UE 100 existing in the vicinity of the UE 100-1.

Third Embodiment

(Operation of Mobile Communication System According to Third Embodiment)

Next, with reference to FIG. 12, an operation of a mobile communicationsystem according to a third embodiment will be described. It is notedthat description will proceed on the basis mainly of a portion differentfrom the above-described embodiments and modifications, and a similarportion will not be described, where necessary

In the above-described second embodiment, a case is described where eachof the UE 100-1 and the UE 100-2 establishes a connection with the eNB200. In the present embodiment, a case is described where each of the UE100-1 and the UE 100-2 does not establish a connection with the eNB 200at first.

FIG. 12 is a sequence diagram showing an operation example of the mobilecommunication system according to the third embodiment.

As shown in FIG. 12, each of the UE 100-1 and the UE 100-2 does not yetestablish a connection with the eNB 200. That is, the UE 100-1 and theUE 100-2 are in an idle state.

As shown in FIG. 12, in step 401, the eNB 200 transmits the Discoveryrelated information into the system information block. Each of the UE100-1 and the UE 100-2 receives the Discovery related information.

In step 402, the UE 100-1 and the UE 100-2 implement the Discovery. Inthe present embodiment, the UE 100-1 (or the UE 100-2) transmits theDiscovery signal corresponding to the Discovery related information.

In step 403, each of the UE 100-1 and the UE 100-2 requests a connectionset-up to the eNB 200. Further, each of the UE 100-1 and the UE 100-2transmits the request for the connection set-up, the request for the D2Dcommunication, and the D2D terminal discovery information. The eNB 200receives the request for the connection set-up, the request for the D2Dcommunication, and the D2D terminal discovery information.

The eNB 200 that receives the request for the connection set-up performsa process for establishing the radio connection with each of the UE100-1 and the UE 100-2.

In the present embodiment, each of the UE 100-1 and the UE 100-2transmits the request for the connection set-up and informationindicating the establishment of the radio connection in order to performonly the D2D communication.

In step 404, the radio connection between the eNB 200 and the UE 100-2is established. Further, the radio connection between the eNB 200 andthe UE 100-1 is established.

Step 405 to step 410 correspond to step 307 to step 312 in the secondembodiment, respectively.

(Operation of Mobile Communication System According to Modification ofThird Embodiment)

Next, with reference to FIG. 13, an operation of a mobile communicationsystem according to a modification of the third embodiment will bedescribed. It is noted that description will proceed on the basis mainlyof a portion different from the above-described embodiment andmodification, and a similar portion will not be described, wherenecessary

In the above-described third embodiment, a case of the two UEs 100 (theUE 100-1 and the UE 100-2) is described. In the present modification, acase of three UEs 100 (the UE 100, the UE 100-2, and UE 100-3) will bedescribed.

FIG. 13 is a sequence diagram showing an operation example of the mobilecommunication system according to the modification of the thirdembodiment.

As shown in FIG. 13, each of the UE 100-1, the UE 100-2, and the UE100-3 does not yet establish a connection with the eNB 200.

As shown in FIG. 13, in step 501, the eNB 200 transmits the Discoveryrelated information into the system information block. The UE 100-1, theUE 100-2, and the UE 100-3 receive the Discovery related information.

In step 502, each of the UE 100-1, the UE 100-2, and the UE 100-3requests the connection set-up to the eNB 200. The eNB 200 that receivesthe request for the connection set-up performs a process forestablishing the radio connection with each of the UE 100-1, the UE100-2, and the UE 100-3.

In step 503, the radio connection between the eNB 200 and the UE 100(the UE 100-1, the UE 100-2, and the UE 100-3) is established.

In step 504, the UE 100-1, the UE 100-2, and the UE 100-3 implement theDiscovery.

In step 505, each of the UE 100-1, the UE 100-2, and the UE 100-3implements the measurement.

In step 506, each of the UE 100-1, the UE 100-2, and the UE 100-3transmits the request for the D2D communication, the terminalmeasurement information, and the D2D terminal discovery information. TheeNB 200 receives the request for the D2D communication, the terminalmeasurement information, and the D2D terminal discovery information.

In step 507, the eNB 200 determines whether the UE 100-1, the UE 100-2,and the UE 100-3 are caused to perform the D2D communication.

In the present embodiment, description proceeds with an assumption of acase where the eNB 200 determines that the interference to the eNB 200when the UE 100-1 and the UE 100-2 perform the D2D communication doesnot exceed the permissive amount, and determines that the interferenceto the eNB 200 when the UE 100-3 performs the D2D communication exceedsthe permissive amount.

In step 508, the eNB 200 instructs each of the UE 100-1 and the UE 100-2to start the D2D communication. That is, the eNB 200 instructs only theUE 100-1 and the UE 100-2 determined that the interference to the eNB200 does not exceed the permissive amount to start the D2Dcommunication.

Each of the UE 100-1 and the UE 100-2 receives the instruction to startthe D2D communication.

In step 509, the eNB 200 transmits information indicating that the D2Dcommunication is not permitted, to the UE 100-3. The UE 100-3 receivesthe information indicating that the D2D communication is not permitted.

In step 510, the UE 100-1 and the UE 100-2 perform the D2Dcommunication.

It is noted that the eNB 200 may instruct the UE 100-3 to performcommunication that passes through the core network (so-called cellularcommunication) with the UE 100-1 and the UE 100-2, and may instruct theUE 100-3 to communicate in a Locally Routed mode.

(Summary of Third Embodiment)

In the present embodiment, the information indicating that when the UE100-1 and the UE 100-2 do not establish the radio connection with theeNB 200 and each of the UE 100-1 and the UE 100-2 establishes the radioconnection in order to perform only the D2D communication istransmitted, together with the request for the connection set-up. As aresult, it is possible to omit transmission and reception of informationwhich is necessary for establishing a normal radio connection and whichis not necessary in the establishment of a radio connection forperforming only the D2D communication.

In the present embodiment, the eNB 200 instructs only the UE 100-1 andthe UE 100-2 determined that the interference to the eNB 200 does notexceed the permissive amount to start the D2D communication, out of theUE 100-1, the UE 100-2, and the UE 100-3. As a result, it is possible toeffectively utilize the D2D communication and restrain the eNB 200 fromreceiving the interference caused by the D2D communication.

Other Embodiments

Thus, the present disclosure has been described with the embodiments.However, it should not be understood that those descriptions anddrawings constituting a part of this disclosure limit the presentdisclosure. From this disclosure, a variety of alternate embodiments,examples, and applicable techniques will become apparent to one skilledin the art.

In the above-described first embodiment, the eNB 200 requests theterminal measurement information and requests the UE 100-1 and the UE100-2 to implement the Discovery; however, this is not limiting. The eNB200 may request the implementation of the Discovery, separately of therequest for the terminal measurement information. For example, when eachof the UE 100-1 and the UE 100-2 performs the D2D communication, the eNB200 may request the implementation of the Discovery after determiningthat the interference to the eNB 200 does not exceed the permissiveamount. In this case, each of the UE 100-1 and the UE 100-2 transmitsthe terminal measurement information, and then, implements the Discoveryafter receiving the request for implementing the Discovery.

Further, in the above-described first embodiment, the eNB 200 transmitsthe request for the terminal measurement information and transmits theconfirmation information; however, this is not limiting. The eNB 200 maytransmit the confirmation information after receiving the terminalmeasurement information. That is, the eNB 200 may transmit theconfirmation information to the UE 100, when determining that the UE100-1 and the UE 100-2 are caused to perform the D2D communication. Itis noted that the eNB 200 may not transmit the confirmation information.

Further, in the above-described first embodiment, each of the UE 100-1and the UE 100-2 transmits the terminal measurement information and theD2D terminal discovery information; however, this is not limiting. Eachof the UE 100-1 and the UE 100-2 may transmit the D2D terminal discoveryinformation, separately of the request for the terminal measurementinformation.

Further, in the above-described first embodiment, each of the UE 100-1and the UE 100-2 transmits the terminal measurement information and theconsent information; however, this is not limiting. Each of the UE 100-1and the UE 100-2 may transmit the consent information, separately of therequest for the terminal measurement information.

It is noted that each of the UE 100-1 and the UE 100-2 may not transmitthe consent information.

Further, in the above-described first embodiment, the eNB 200 determineswhether the UE 100-1 and the UE 100-2 are caused to perform the D2Dcommunication on the basis of the terminal measurement information, theD2D terminal discovery information, and the consent information;however, this is not limiting.

For example, the eNB 200 may omit the determination based on the consentinformation. Further, the eNB 200 may omit the determination based onthe D2D terminal discovery information. That is, the eNB 200 maydetermine whether the UE 100-1 and the UE 100-2 are caused to performthe D2D communication on the basis only of the terminal measurementinformation. In this case, the eNB 200 may instruct the start of the D2Dcommunication, and request the implementation of the Discovery.

Further, in the above-described second embodiment, the eNB 200 may notexplicitly request the UE 100 to transmit the new terminal measurementinformation different from the old terminal measurement information. Forexample, the UE 100 may transmit the new terminal measurementinformation in a predetermined cycle, even when there is no explicitrequest from the eNB 200.

Further, in the above-described third embodiment, each of the UE 100-1and the UE 100-2 transmits, in addition to the request for theconnection set-up, the request for the D2D communication and the D2Dterminal discovery information; however, this is not limiting. Each ofthe UE 100-1 and the UE 100-2 may individually transmit the request forthe connection set-up, the request for the D2D communication, and theD2D terminal discovery information.

Further, in the modification of the above-described third embodiment,each of the UE 100-1, the UE 100-2, and the UE 100-3 transmits therequest for the D2D communication, the terminal measurement information,and the D2D terminal discovery information; however, this is notlimiting. Each of the UE 100-1, the UE 100-2, and the UE 100-3 mayindividually transmit the request for the D2D communication, theterminal measurement information, and the D2D terminal discoveryinformation.

Further, in the above-described embodiments, the eNB 200 determineswhether the UE 100-1 and the UE 100-2 are caused to perform the D2Dcommunication; however, this is not limiting. Further, the eNB 200determines whether each of the UE 100-1 and the UE 100-2 supports theD2D communication; however, this is not limiting. For example, MME/S-GW300, that is an upper device of the eNB 200, may perform thedetermination.

Further, in the above-described embodiments, the eNB 200 may notify, byunicast or broadcast, the UE 100 of information to the effect that D2Dcommunication under the control of the cell of the eNB 200 is permitted.

Further, in the above-described embodiments, the eNB 200 may instructthe UE 100 to start the D2D communication when the D2D communication isperformed only in a state where the UE 100 establishes the radioconnection (RRC connection) with the eNB 200. According thereto, as inthe modification of the above-described first embodiment, when it isdetermined that the UE 100 that performs the D2D communication gives theinterference to the eNB 200, the eNB 200 is capable of instructing theUE 100 that performs the D2D communication to end the D2D communication.The eNB 200 may notify the UE 100, by unicast or broadcast, of the UE100 performing the D2D communication only in a state where the UE 100establishes the radio connection with the eNB 200.

It is noted that exceptionally, when there is no UE 100 camping on thecell 250 managed by the eNB 200 or when the UE 100 needs to urgentlyperform the D2D communication, the eNB 200 may instruct the UE 100 tostart the D2D communication without establishing the radio connectionwith the eNB 200.

Further, in the above-described embodiments, the UE 100 may transmit ameasurement report as the terminal measurement information.

Further, in the above-described embodiments, when determining whetherthe interference to the eNB 200 does not exceed the permissive amount byusing the above-described determination method A1, the eNB 200 maydetermine whether the interference from the UE 100 to the eNB 200 doesnot exceed the permissive amount on the basis only of the minimumdistance, out of the distance X1 and the distance X2. Upon determinationon the basis of the minimum distance when determining that theinterference from the UE 100 to the eNB 200 does not exceed thepermissive amount, the eNB 200 is capable of determining for all the UEs100 that the interference to the eNB 200 does not exceed the permissiveamount.

Further, in the above-described embodiments, when determining whetherthe interference from the UE 100 to the eNB 200 does not exceed thepermissive amount, the eNB 200 may determine whether the interferencefrom the UE 100 to the eNB 200 does not exceed the permissive amount onthe basis not only of the pathloss information from the UE 100 to theeNB 200 but also of the terminal measurement information.

Further, in the above-described first embodiment, the eNB 200 transmitsthe request for the terminal measurement information and transmits theconfirmation information; however, this is not limiting. The eNB 200 maytransmit the confirmation information after receiving the terminalmeasurement information. That is, the eNB 200 may transmit theconfirmation information to the UE 100, when determining that the UE100-1 and the UE 100-2 are caused to perform the D2D communication.

Further, in the above-described embodiments, when determining that theinterference to the eNB 200 exceeds the permissive amount in performingor being performing the D2D communication, the eNB 200 may notify, byunicast or broadcast, the UE 100 of the information indicating that theD2D communication is not permitted.

Naturally, each of the above-described embodiments and modifications maybe combined, where necessary.

In the above-described embodiments, an example in which the presentdisclosure is applied to the LTE system has been described. However, thepresent disclosure may also be applied to systems, other than the LTEsystem, as well as the LTE system.

INDUSTRIAL APPLICABILITY

As described above, the mobile communication system, the base station,the user terminal, and the processor according to the present disclosureare able to restrain interference to a base station by a user terminalthat performs D2D communication, and thus are useful for a mobilecommunication field.

The invention claimed is:
 1. A communication system, comprising: a userterminal; and a base station, wherein the user terminal transmits UEEUTRA capability information including information indicating an onlyuplink band on which the user terminal supports direct communicationbetween terminals, to the base station, to enable the base station todetermine, on the basis of the UE EUTRA capability information, whetherthe user terminal supports the direct communication, the user terminalreceives, from the base station, information on radio resources toperform the direct communication, and the user terminal controls:starting the direct communication based on the received information onradio resources; measuring Reference Signal Received Power (RSRP) of areceived signal from the base station during performing the directcommunication; and ending the direct communication in response to theRSRP being higher than a predetermined value.
 2. A user terminal,comprising: a transmitter; a receiver; and a controller; wherein thetransmitter is configured to transmit UE EUTRA capability informationincluding information indicating an only uplink band on which the userterminal supports direct communication between terminals, to abasestation, to enable the base station to determine, on the basis of the UEEUTRA capability information, whether the user terminal supports thedirect communication, the receiver is configured to receive, from thebase station, information on radio resources to perform the directcommunication, and the controller is configured to control: starting thedirect communication based on the received information on radioresources; measuring Reference Signal Received Power (RSRP) of areceived signal from the base station during performing the directcommunication; and ending the direct communication in response to theRSRP being higher than a predetermined value.
 3. A processor,communicatively coupled to a memory, and configured to controlling for auser terminal, wherein the processor executes processes of: transmittingUE EUTRA capability information including information indicating an onlyuplink band on which the user terminal supports direct communicationbetween terminals, to a base station, to enable the base station todetermine, on the basis of the UE EUTRA capability information, whetherthe user terminal supports the direct communication; receiving, from thebase station, information on radio resources to perform the directcommunication; controlling starting the direct communication based onthe received information on radio resources; controlling measuringReference Signal Received Power (RSRP) of a received signal from thebase station during performing the direct communication; and controllingending the direct communication in response to the RSRP being higherthan a predetermined value.